java - 无法从 JTextField 获取整数

Question

我试图从 JTextField 获取整数，但我不断收到 NumberFormatException。我使用了下面的代码:

JTextField price = new JTextField();
price.addActionListener(new ComboListener());
String inputText = price.getText();
int inputPrice = Integer.parseInt(inputText);

每个网站都说这是正确的方法，所以我不明白我做错了什么。

编辑:完整代码在这里:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class RatePanel extends JPanel {

    private double[] rate; // exchange rates
    private String[] currencyName;
    private JLabel result;

    public RatePanel() {
        currencyName = new String[]{"Select the currency..",
            "European Euro", "Canadian Dollar",
            "Japanese Yen", "Australian Dollar",
            "Indian Rupee", "Mexican Peso"};

        rate = new double[]{0.0, 1.2103, 0.7351,
            0.0091, 0.6969, 0.0222, 0.0880};

        JLabel title = new JLabel("How much is that in dollars?");
        title.setAlignmentX(Component.CENTER_ALIGNMENT);
        title.setFont(new Font("Helvetica", Font.BOLD, 20));
        add(title);
        add(Box.createRigidArea(new Dimension(0, 100)));
        JLabel enter = new JLabel("Enter cost of item");
        enter.setAlignmentX(Component.LEFT_ALIGNMENT);
        enter.setFont(new Font("Helvetica", Font.BOLD, 20));
        add(enter);
        JTextField price = new JTextField();
        price.addActionListener(new BoxListener());
        price.setAlignmentX(Component.RIGHT_ALIGNMENT);
        add(price);
        add(Box.createRigidArea(new Dimension(0, 100)));
        JLabel select = new JLabel("Select a currency: ");
        select.setAlignmentX(Component.LEFT_ALIGNMENT);
        select.setFont(new Font("Helvetica", Font.BOLD, 20));
        add(select);
        JComboBox Cbox = new JComboBox(currencyName);
        Cbox.addActionListener(new ComboListener());
        Cbox.setAlignmentX(Component.RIGHT_ALIGNMENT);
        add(Cbox);
        String index = Cbox.getSelectedItem().toString();
    }

    public class BoxListener implements ActionListener {

        public void actionPerformed(ActionEvent event) {
            String inputText = price.getText();
            int inputPrice = Integer.parseInt(inputText);
        }
    }

    public class ComboListener implements ActionListener {

        public void actionPerformed(ActionEvent event, String index, double inputPrice, double[] rate) {
            double finalPrice = 0;
            switch (index) {
                case "European Euro":
                    finalPrice = inputPrice * rate[1];
                    break;
                case "Canadian Dollar":
                    finalPrice = inputPrice * rate[2];
                    break;
                case "Japanese Yen":
                    finalPrice = inputPrice * rate[3];
                    break;
                case "Australian Dollar":
                    finalPrice = inputPrice * rate[4];
                    break;
                case "Indian Rupee":
                    finalPrice = inputPrice * rate[5];
                    break;
                case "Mexican Peso":
                    finalPrice = inputPrice * rate[6];
                    break;
            }

            result = new JLabel(inputPrice + "USD equals " + finalPrice
                    + index);
            add(result);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            throw new UnsupportedOperationException("Not supported yet.");
        }
    }
}

Answer 1

我运行了你的代码，它实际上工作得很好(没有给我 NumberFormatException)。

您收到 NumberFormatException 可能是因为您尝试了以下操作:

1. 当文本字段为空时按 Enter
2. 当文本字段包含非数字输入时，在文本字段上按 Enter

在尝试将文本字段的内容解析为整数之前，您可以向输入添加验证:

public class BoxListener implements ActionListener {

    public void actionPerformed(ActionEvent event) {
        String s= price.getText();
        if(s.matches("[0-9]+"))               //Perform validation before parsing string
            inputPrice = Integer.parseInt(s);
    }
}

另请注意，我没有将 inputPrice 和其他组件(例如文本字段)声明为局部变量，而是将它们声明为 RatePanel 的实例变量。

<小时/>

将变量声明为实例变量而不是局部变量:

class RatePanel extends JPanel{
    private JTextfield txtPrice;   // <--- declare here as instance variable
    private int inputPrice;        // <--- declare here as instance variable

    public RatePanel(){
        //If you declare in the constructor or other methods, they become local variables.
    }
}